The intake combustion air is burdened to a great extent with coarse dirt particles when using work tools such as motor-driven chain saws, cutoff machines and the like driven by internal combustion engines. These coarse dirt particles can lead to a quick clogging of the main filter. For this reason, a prefilter is used which keeps the coarse dirt particles away from the main filter.
As a prefilter, it is known to use collars made of foam material, felt or the like which cover the outer surface of the main filter and which are intended to keep the coarse dirt particles away from the main filter. However, these prefilters restrict the air throughput and tend to become clogged quickly because of their fine porous configuration. These prefilters must therefore often be cleaned or exchanged.
The prefilter used must furthermore resist also the effects of fuel and heat which affect the firm seating of the prefilter on the filter ring (filter cartridge).